Wheelchairs are land vehicles that are provided for transporting the physically impaired. Wheelchairs generally include a base frame supported on a supporting surface by a pair of idler wheels and a pair of drive wheels. The drive wheels may be manually driven by a wheelchair occupant or power driven by motors controlled by the wheelchair occupant. The wheelchair may be maneuvered by differentially driving the drive wheels. The idler wheels are generally in the form of casters which swivel to further enhance the maneuverability of the wheelchair.
The drive wheels have historically been supported by a rear portion of the wheelchair base frame while casters have been supported by a front portion of the wheelchair. However, the drive wheels of late have been supported by a front portion of the base frame as well. The former wheelchairs are commonly referred to as rear-wheel drive wheelchairs while the later wheelchairs are commonly referred to as mid-wheel drive wheelchairs. The casters of rear-wheel drive wheelchairs are typically located towards the front of the base frame. Conversely, the casters of mid-wheel drive wheelchairs are typically located towards the rear of the base frame.
Tipping is an inherent problem with wheelchairs that occurs when accelerating or traversing obstacles. Tipping may also occur in wheelchairs that are provided with reclining seats. Anti-tip wheels are commonly attached to wheelchairs to reduce the risk of wheelchairs tipping over. Anti-tip wheels are usually attached to the rear end of rear-wheel drive wheelchairs and to the front end of mid-wheel drive wheelchairs. In either case, the drive wheels are disposed between the casters and the anti-tip wheels. This may have an undesirable affect on the operation of the wheelchair. For example, if the front casters and the anti-tip wheels each simultaneously encounter an obstacle having sufficient elevation, the drive wheels may lose contact with the ground and thus, lose its ability to move the wheelchair. This could render a wheelchair occupant stranded.
Resilient anti-tip wheel suspensions have been provided in an effort to overcome the foregoing problem. Resilient anti-tip wheel suspensions permit displacement of the anti-tip wheels when obstacles are encountered to reduce the risk of the drive wheels losing contact with the ground. However, resilient anti-tip wheel suspensions have a limited effect on reducing the risk of wheelchairs tipping over when the wheelchairs tip too far rearward. This is especially true for wheelchairs having a reclining seat.
Moreover, resilient anti-tip wheel suspensions commonly rotate about a fixed transverse axis. The fixed transverse axis of rotation may limit the mobility of the wheelchair. For example, anti-tip wheels in the form of casters swivel about an axis to change direction in response to the movement of the wheelchair. As an anti-tip wheel suspension rotates about a fixed transverse axis, the swivel axis may deviate from a vertical orientation. That is to say, as an anti-tip caster changes in elevation, the swivel axis moves along an arcuate path. This causes the caster to lose its ability to swivel. This hinders the wheelchair occupant""s ability to negotiate obstacles while changing the direction in which the wheelchair is moving.
A resilient anti-tip wheel suspension is needed that maintains a caster in a substantially vertical orientation throughout movement of the wheelchair over obstacles and uneven terrain.
This invention is directed towards a resilient anti-tip wheel suspension that maintains a caster in a substantially vertical orientation throughout movement of a wheelchair over obstacles and uneven terrain. The resilient anti-tip wheel suspension comprises a wheel coupled to a first mounting bracket. A second mounting bracket is adapted to be rigidly mounted to a wheelchair. Upper and lower bars each have front and rear ends that are pivotally connected to the second mounting bracket and the first mounting bracket, respectively, so as to form a parallelogram configuration.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.